Traditionally, the cab signal receivers on board of railway and mass and/or rapid transit vehicles are tested daily prior to placing a train in revenue service or regular operation. Previously, the method of testing the sensitivity and integrity of the cab signal receiver was to position the pickup coils over a suitable wire loop or track circuit so that test signals fed into the loop or track were inductively coupled to the pickup coils. Thus, in the past, it was necessary either to physically place a pair of inductive loops of a portable test set under the car-carried receiver pickup coils or to move the front end of the vehicle onto the track circuit or over a fixed test loop in a permanent installation.
In either case, it is both time consuming and expensive to initially set up an indirectly coupled cab signal test facility. In addition, previous code test sets were bulky as well as complex due to a multitude of components and circuitry. For example, each of the code rates required a separative active oscillating circuit for selectively coding the carrier signal. In one instance, an eighty foot (80') length of wire was laid between the rails of the test track to form the inductive loop to carry the simulated track current. In another case, a pair of inductive coils had to be physically and precisely positioned beneath the pickup coils of each locomotive or lead car prior to conducting the cab signal tests. It will be appreciated that the power requirement of inductive types of test sets must be equivalent to that of the wayside cab signal transmitters which are comparatively large when the induced pickup current range is between 1.3 and 1.6 amperes. A further problem encountered in inductive types of code testing was due to the large amount of iron and steel in a railway environment which causes inconsistent test results. Thus, there is a valid need for improving and simplifying the method and apparatus for more effective and efficient departure testing cab signal equipment.